The temperature of a liquid is being measured by a line operator. Which is least likely to be influenced by the instrument?

In Measurement System Analysis (MSA), total variation is broken down into components, including the instrument (gage), the operator (appraiser), and the part itself. The instrument directly produces a reading (D) and its performance is maintained through calibration (C). The instrument also has a physical effect on the system being measured; for instance, a thermometer can slightly alter the temperature of the liquid it is measuring (B). However, the act of recording the measurement is a distinct step performed by the operator after observing the instrument's reading. Errors in this step, such as transcription mistakes, are classified as operator or human errors, not instrument errors. Therefore, the recording of the measurement is the activity least likely to be directly influenced by the instrument's intrinsic characteristics.

B. The instrument's presence can alter the actual temperature of the liquid through heat exchange, a direct physical influence.
C. Calibration is the process of adjusting an instrument based on its performance against a standard; it is entirely dependent on the instrument's properties.
D. The reading is the direct output value provided by the instrument and is completely determined by its design, condition, and interaction with the substance.

1. Montgomery, D. C. (2020). Introduction to Statistical Quality Control (9th ed.). Wiley. In Chapter 8, "Gage and Measurement System Capability Studies," Section 8-2 discusses the sources of variability in measured data, making a clear distinction between variability arising from the instrument (gage) and the operator (appraiser). Operator actions like recording are treated separately from the instrument's inherent properties.

2. University of Cambridge, Department of Engineering. (n.d.). Experimentation and Measurement: An Introduction for Engineers. In Section 2.3, "Sources of Error," a distinction is made between systematic/random errors (often related to the instrument) and illegitimate errors or blunders, which include "misreading a scale" and "writing down the wrong value." This classifies recording as a human action separate from the instrument's influence. (Available through University of Cambridge course materials).

3. JCGM 100:2008, Evaluation of measurement data — Guide to the expression of uncertainty in measurement (GUM). Section 3.1.6 defines "indication" as the value provided by the instrument. The guide's framework for evaluating uncertainty treats the instrument's indication as a distinct input, separate from any subsequent human actions like recording or data processing, which would be considered additional stages in the measurement model.